Facebook is widely expected to unveil a homescreen for smartphones tomorrow at an event in California.

The social media giant has refused to divulge any further details relating to the launch beyond promising a "product announcement", with the invitation asking guests to "come see our new home on Android".

The event has already generated widespread interest online, where much speculation surrounds the rumoured Facebook homescreen which analysts suggest would run on Google's mobile operating system Android.

Leaked images of what is claimed to be a "Facebook phone" have also appeared on websites, feeding theories that the social network could showcase a new HTC mobile made with integrated Facebook features.

Stuart Miles, founder of technology and gadget site Pocket-lint, says: "My initial thought was that they couldn't possibly be launching a phone because that would be silly, because every phone is already a Facebook phone.

"I think ultimately this will be an enhanced app that you can run from your homescreen on Android which will give you the feeling that your phone is a Facebook phone."

The launch of an "enhanced app" would reinforce Facebook's "mobile first" attitude, he said, as users increasingly monitor the social networking site from smartphones and tablets, rather than desktop computers.

According to the site, more than 680 million of its one billion users now check Facebook from mobile devices.

Ernest Doku, telecoms expert at comparison site uSwitch.com, says the arrival of a "Facebook phone" would mark a new departure for mobile devices.

"After a protracted journey to market, the 'Facebook phone' finally seems set to arrive," he says. "The device is a concerted bid for Facebook to make a play for the eyeballs of millions of consumers, and become the hub from which they interact with all aspects of their smartphone.

"The important word on Facebook's invitation is 'home'. We should expect Facebook to greet mobile users when they turn their smartphones on in the morning, and to be the core of the user's experience; integral to searching, surfing and interacting."

He adds: "This forthcoming device will be the tip of the spear, a focused showcase of what is possible with deeper Facebook integration, and is certain to mark the start of future devices which embed the social network into the fabric of functionality, from a number of manufacturers."

Both Facebook and HTC have refused to comment on the speculation surrounding the announcement. Tomorrow's launch event will be broadcast live online at around 6pm.